For backpackers, it’s a treat to escape civilization and traverse through the woods, enjoying the ruggedness of the great outdoors. But carrying that heavy backpack for days can undoubtedly be a drag.
One group of researchers in China has some welcome news: an invention aimed at lightening the load. They’ve designed a new backpack that accounts for the inertial forces of the bag against a backpacker’s body as the person walks, reducing the metabolic energy demand on the user by an average of 11 percent. Their design is described in a study published 27 July in IEEE Transactions on Neural Systems and Rehabilitation Engineering.
Caihua Xiong, a professor at Huazhong University of Science and Technology who was involved in the study, notes that humans around the world and across the ages have been exploring ways to lighten their loads. “Asian people utilized flexible bamboo poles to carry bulky goods, and Romans designed suspended backpacks to carry heavy loads, which show energetic benefits,” he notes. “These designed passive carrying tools have the same principle [as ours].”
As humans walk, our gait is particularly energy efficient when only one foot is on the ground. But when we transition to the other foot and both are temporarily grounded, this is where the energy transfer becomes less efficient. And if we are carrying a heavy backpack, the extra inertial force from the backpack’s vertical movement and oscillations creates further inefficiencies during this transition.
To adjust for these inertial forces, Xiong’s team designed a motorized backpack that has two different modes. In its passive mode, two symmetrically arranged elastic ropes balance the weight of load within the backpack. When the user turns on the system’s active mode, a rotary motor regulates the acceleration of load. The backpack, which weighs 5.3 kilograms, was designed to carry loads up to 30 kg.
In experiments with seven similarly sized men, the researchers compared the energy requirements of using a typical rucksack to those of their new backpack system (in both its active and passive modes). Each of the participants was asked to try these three scenarios in random order, while respiratory measurements and surface electromyography signals from their leg muscles and were taken to analyze their energy expenditures.
The motorized backpack in active mode reduced the load acceleration by 98.5 percent on average. This decreased the energy demand on the user by 11 percent compared with the conventional rucksack. The energy savings in passive mode came in at 8 percent on average. Xiong cautions that these reductions may in part be due to the distribution of weight within the two backpacks, since the designed system has the motor in a fixed position higher in the backpack. In contrast, the contents of the rucksack are loose in the compartment and thus the weight distribution compared to the user’s center-of-mass is different.
Also of note: The study involved people walking on flat ground. Xiong says he is interested in potentially commercializing the product, but aims to first explore ways of improving the system for different walking speeds and terrains.
This article appears in the October 2020 print issue as “Motorized Backpack Lightens the Load.”